1. Field of the Invention
The invention relates to a superconducting cable joint.
More specifically, it relates to a joint between two abutting cables, each cable comprising, around a central support, at least one phase layer composed of at least one layer of superconducting material and a neutral layer, these layers being concentric and contained in a shell filled with cryogenic fluid.
2. Description of Related Art
Patent EP 2 006 862 discloses the use of three single-phase cables for each cable and the connection of two abutting cables of the same phase. The two abutting phase layers of superconducting material are then connected by a central conducting element covered with at layer of complementary insulating material.
The invention also relates to cables comprising, around a central support, three concentric phases each composed of at least one layer of superconducting material, these layers being separated by a layer of insulating material.
The assembly formed by each cable may be covered with a screen connected to neutral and with an outer sheath, as described in US 2010/0184604. These cables are contained in a shell filled with cryogenic fluid, generally liquid nitrogen. The latter document describes a complex cable joint which is time-consuming to produce, being formed by reconstituting the layers of superconducting material, and the layers of insulating material by means of an arrangement in stages with superimposition.
The invention relates to a joint between two abutting cables, each cable comprising, around a central support, at least one phase layer composed of at least one layer of superconducting material and a neutral layer, these layers being concentric, the joint being reliable and easily produced.
For this purpose, the invention proposes a joint between two abutting cables, each cable comprising, around a central support, at least one phase layer composed of at least one layer of superconducting material and a neutral layer, these layers being concentric and contained in a shell filled with cryogenic fluid, said abutting inner phase layers being stripped and being directly connected, characterized in that said neutral layer of each cable is also stripped, at least one bridging support member is placed between said stripped neutral layers, and a layer of conducting or superconducting material for electrically connecting these neutral layers is placed on said bridging support member.
In a preferred embodiment, said support member is formed by a bridging element of tubular insulating material beveled at its ends.
Very advantageously, a longitudinal cylindrical space filled with cryogenic fluid is provided between the joint of said inner phase layers of superconducting material and the bridging support member.
In this embodiment, the forming of the joint, makes use of the dielectric properties of the cryogenic fluid contained in the enclosure.
Said bridging support members may be made at least partially of metal and/or at least partially of insulating material.
Preferably, each cable comprises, around a central support, three concentric phase layers, each composed of at least one layer of superconducting material and a neutral layer, these layers being separated by a layer of insulating material, the innermost abutting phase layers being stripped and directly connected, and said layers of superconducting material are stripped in a staged way, from the innermost phase to the neutral, moving away from the joint end, while a bridging support member is placed between each stripped phase or neutral layer and the other same layer, and a layer of conducting or superconducting material for the electrical connection of the same phase or neutral layers is placed on each support member.
In a preferred embodiment, said support members are each formed by a bridging element of tubular insulating material beveled at its ends.
Very advantageously, a longitudinal tubular space filled with cryogenic fluid is provided between said innermost, phase layers of superconducting material and the subsequent bridging support member, and a longitudinal, tubular space filled with cryogenic fluid is also provided between each bridging support member and each said layer of conducting or superconducting electrical connection material placed on the innermost bridging support member.
Said bridging support members may be made at least partially of metal and/or at least partially of insulating material.
Said insulating material is preferably paper.
Said metal is preferably aluminum or stainless steel.
Very advantageously, said bridging support members are prefabricated.
This prefabrication is particularly advantageous because it enables the joint to be produced very rapidly and easily and also allows a high degree of safety to be achieved, particularly at high voltage, as the prefabricated elements have precise shapes and dimensions which are independent of human error or approximation.
Preferably, each said layer of conducting or superconducting electrical connection material is formed from strands or tapes laid in a distributed manner on said bridging element.
Also advantageously, each said electrical connection layer is made of superconducting material.
Thus the electrical connections throughout the joint are practically exclusively superconducting, since the connection resistance between the strands or tapes is extremely low at cryogenic temperatures. The joint therefore provides virtual continuity of the superconducting property of the cable with virtually no Joule effect losses. In the first place, this enables the losses of the system to be reduced; furthermore, it can considerably reduce the risk of local heating compared with a resistive connection which could cause a local transition of the cable outside its critical temperature, possibly resulting in destruction.
Moreover, the overall dimensions of this connection using superconducting copper strands or tapes are smaller than those of the same connection using resistive copper tapes or strands.